Fast curing phenolic resin for making plywood

ABSTRACT

A phenol-formaldehyde resole resin solution useful in adhesives for preparing wood laminates from a plurality of wood veneers, prepared by reacting at least an equal molar amount of formaldehyde with phenol in the presence of sodium hydroxide and a water-soluble potassium salt selected from the group consisting of potassium chloride, potassium sulfate and mixtures thereof.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention broadly relates to an improved phenolic resin compositionuseful in adhesives for making composite wood products, particularlyplywood. The invention also relates to a process for making plywood.

2. Description of Related Art

Phenolic resin-based adhesives are well-known for their exceptionalstrength and durability. Such resins have achieved wide spreadacceptance in the United States and elsewhere as the principal componentof adhesives used in making wood laminates such as plywood, particularlyfor exterior exposure. Phenolic resins for use in such adhesivesgenerally are prepared by condensing phenol with a molar excess offormaldehyde under alkaline reaction conditions. The resulting resins,typically referred to as resoles, are thermosetting polymers oroligomers.

For producing plywood, the adhesive is applied to the mating surfaces ofwood veneers and the veneers are subjected to a pressing operation at anelevated temperature to consolidate them into a unitary panel and tocure the adhesive. Often, the pressing is performed in two stages tomaximize output; using a first or pre-press stage at ambient temperatureand under a pressure and for a time just sufficient to consolidate theveneers into a unitary panel. The consolidated panel can be stored andhandled without shifting or separation of the veneers and afterwards canbe treated under heat and pressure to cure the thermosetting adhesiveand form the final laminate.

One recognized draw back of conventional phenol-formaldehyde resins istheir slow rate of cure.

In preparing wood laminates such as plywood with such adhesives, it haslong been conventional to dry the wood veneers to a very low moisturecontent, i.e., to less than about 5% average moisture content (5 lbs.water/100 lbs. dry wood), before application of the adhesive andconsolidation of the veneers. Use of high moisture content veneers withadhesives formulated with conventional phenolic resins invariably leadsto a large number of lamination defects and an excessively large numberof rejected panels because of poor lamination.

Many lamination defects are believed to be caused by steam formationbetween veneer layers and a blow out of the steam when pressure isreleased upon completion of the pressing cycle. As the temperatureincreases in the center of the veneers during consolidation, so does thevapor pressure of trapped steam. As the press is opened, the built-upvapor or steam seeks an avenue of escape and blows the panel.

Sizable operating and capital costs have been incurred in the prior artto assure consistently low moisture content for wood veneers used inmaking wood laminates such as plywood, and thus eliminate laminationdefects and reduce the number of rejected panels. The prior art,however, has recognized the advantages to be gained in both operatingand capital costs if higher moisture content veneers could be employedin the preparation of wood laminates, and the plywood industry recentlyhas increased its efforts to identify adhesives suitable for bondinghigher moisture content veneers.

In U.S. Pat. No. 4,239,577, for example, a process is described forpreparing wood laminates from high moisture content wood veneers. Inaccordance with this process, panels are prepared using veneers ofdiffering moisture contents with higher moisture content veneersconstituting the outer layers of the consolidated panel and lowermoisture content veneers constituting the panel core. While this processpurports to ameliorate problems encountered when using high moisturecontent veneers with adhesives formulated with conventional phenolicresins, it does not eliminate the need for drying at least some of theveneers to a low moisture content.

In U.S. Pat. No. 4,412,945, an adhesive is described which purportedlypermits the preparation of wood laminates using high moisture contentveneers. The adhesive composition combines a phenol-aldehyde resin, analkaline catalyst and from 5-50%, based on the weight of resin solids,of a bentonite clay. The adhesive also may contain other conventionaladditives such as fillers and extenders. Apparently, this adhesive hasnot received widespread acceptance in the plywood industry, whichcontinues to search for ways to reduce substantially the need to dryhigh moisture content veneers before assembling them into unitary woodlaminates.

Reduced veneer drying requirements result in savings in capital costsand processing time and also lead to improvements in the dimensionalstability of the consolidated wood laminates. Conventional laminatesmade with veneers having less than about 5% moisture content tend toswell in size as the moisture content of the wood laminate increases toits equilibrium content gradually with time. In the summer months, theequilibrium moisture content of a wood laminate may be as high as about10% by wt. Finally, the ability to prepare laminates using high moisturecontent veneers, e.g. about 7 wt. % and higher, also relaxes thecriticality of moisture control in veneer preparation.

Through the years, various other modifications also have been proposedfor producing phenol-formaldehyde resins which exhibit a faster curerate without sacrificing bond strength and quality. Such resins might bebetter suited for bonding veneer of higher moisture content. Thus, theprior art has employed the use of more reactive phenols such asresorcinol, reactive additives such as formamide, or the addition ofvarious cure rate accelerators such as potassium carbonate, just priorto use. Unfortunately, these approaches have not succeeded for a varietyof reasons, including increased costs, inconvenience, and health andsafety considerations.

Daisy et al. U.S. Pat. No. 4,758,478 indicates that by replacing atleast a part of the sodium hydroxide commonly used to preparephenol-formaldehyde condensates, with potassium hydroxide, a fastercuring resin is obtained. The patent further asserts that such apotassium-modified resole resin exhibits improved cure speed without anyloss in rheological properties. Consequently, reduced adhesive spreadsare possible and it is possible to use such resins to prepare adhesivesfor making plywood from veneers of increased moisture content.

Unfortunately, potassium hydroxide is a more expensive source ofalkalinity than sodium hydroxide and thus such resins are more expensivethan their conventional counterparts. Thus, there remains a need in theart for methods for modifying conventional phenolformaldehyde resins toprovide a more economical, faster curing resin suitable for bondingveneers with higher average moisture contents.

Applicant has found that it is possible to prepare a faster curing andmoisture tolerant resole resin, while using sodium hydroxide to supplyall of the alkalinity for preparing the phenolic resin, as has commonlybeen done in preparing phenol-formaldehyde resole resins, by also usinga small amount of certain water-soluble potassium salts selected fromthe group consisting of potassium chloride, potassium sulfate andmixtures thereof. Quite surprisingly, the molecular weight distributionof such a potassium salt-modified phenolic resin is strikingly similarto resins prepared by using a combination of potassium hydroxide andsodium hydroxide.

Thus, resins of the present invention exhibit similar properties tothose prepared using a combination of sodium hydroxide and potassiumhydroxide but are much more economical due to the significantly lowercost for the water-soluble potassium salt additives and the typicallylower amount of such salts which are required to obtain desirable resinproperties relative to the amount of potassium hydroxide needed toobtain a similar resin. Resins of the present invention are particularlysuitable for preparing adhesives used for making plywood, particularlyplywood made from veneers having a relatively high average moisturecontent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 3 show the gel permeation chromatography (GPC) tracesfor resins prepared in accordance with Examples 1 and 2 and ComparativeExample 1, respectively.

DESCRIPTION OF THE INVENTION

The present invention is directed to a potassium salt-modifiedphenol-formaldehyde resole resin useful in adhesives for bondingcellulosic products, particularly for preparing plywood. The presentinvention also is directed to adhesives prepared from such resins, themethod of bonding cellulosic materials using such adhesives and theresultant cellulosic composites. The resin has particular utility formaking plywood adhesives used to bond veneers of relatively high averagemoisture content.

The phenol-formaldehyde resins of the present invention are commonlyreferred to as resoles and constitute thermosetting condensationproducts produced by reacting at least an equal molar amount offormaldehyde with phenol. Particularly preferred phenol-formaldehydecondensation products are prepared using a molar ratio of phenol toaldehyde in the range of about 1:1.5 to 1:3 with a phenol toformaldehyde molar ratio of about 1:2 being particularly preferred.

In preparing resins according to the present invention, formaldehyde isreacted with phenol in an aqueous reaction medium in the presence of thealkaline catalyst. Sodium hydroxide is the alkaline catalyst of choicein the present invention.

A variety of techniques are known in the art for reacting phenol andformaldehyde in the presence of the alkaline catalyst. Typically, theresin is reacted in stages with separate partial additions of either oneor both of the reactants and the alkaline catalyst. For example, onecommon procedure is to react the phenol with a portion of theformaldehyde, in the presence of a portion of the alkaline catalyst.After a brief, initial exothermic reaction, additional amounts ofalkaline catalyst and formaldehyde are added to the reacting mixture andthe reaction is continued with careful control of the reactiontemperature. Once all of the reactants and catalyst have been added, thereaction is allowed to proceed to a suitable end point, which may bedetermined by measuring the refractive index of the reacting mixture orby measuring the viscosity of the reacting mixture of by somecombination thereof as recognized by those skilled in the art. Once theselected end point is achieved, the reaction mixture is cooled and theresin is ready for preparing an adhesive mixture.

An amount of sodium hydroxide is added during the preparation of theresin to produce a resole resin solution having an alkalinity content,i.e. an amount of alkaline catalyst, in the range of about 1% to about15%, preferably about 3% to about 9%, and most preferably about 4% toabout 8% based on the weight of the resole resin solution. As usedherein alkalinity content means the content of alkaline catalystexpressed as a percent of a solution according to the equivalent weightof sodium hydroxide. Normally, from about 50 mol % of sodium hydroxideup to about 100 mol % of sodium hydroxide based on the mols of phenolused in preparing the resole resin will provide the desired level ofalkalinity. Preferably about 0.60 mol to about 0.80 mol of sodiumhydroxide per mol of phenol is used.

Preferably, hydroxybenzene (phenol) is the phenol reactant of choice,although substituted phenols such as cresol and higher functionalphenols such as resorcinol or bisphenol-A, can be used. Formaldehyde isthe preferred aldehyde constituent. Generally, the formaldehyde issupplied as an aqueous solution known in the art as "formalin". Formalingenerally contains from about 37% to about 50% by weight formaldehyde.Other forms of formaldehyde such as paraformaldehyde also can be used.Other aldehydes, which may be used in lieu of or in combination withformaldehyde, include aliphatic aldehydes such as acetaldehyde andpropionaldehyde; aromatic aldehydes such as benzylaldehyde and furfuraland other aldehydes such as aldol, glyoxal and crotonaldehyde.

In accordance with the present invention, a water-soluble potassium saltselected from the group consisting of potassium chloride, potassiumsulfate and mixtures thereof is included at some point during thepreparation of the resole resin. For convenience, the potassium salt isone of the ingredients present when reaction conditions are established.Generally, resins according to the present invention are prepared byadding from about 1 mol % up to about 25 mol %, preferably from about 3mol % up to about 20 mol %, and most preferably from about 5 mol % up toabout 15 mol % of potassium via use of a potassium salt selected fromthe group consisting of potassium chloride, potassium sulfate andmixtures thereof based on the mols of phenol used in preparing theresole resin. Higher levels of potassium addition do not appear toimprove the properties of the resins sufficiently to justify theadditional costs; whereas at lower levels of potassium addition thebeneficial impact from using the water soluble potassium salt islessened. In general, at least about 3 mol % of potassium based on themolar amount of phenol used in preparing the resin, is included toproduce a noticeable enhancement in the resin's of properties relativeto a resole resin prepared using only sodium hydroxide. Amounts aboveabout 20 mol % based on the moles of phenol used, is generally notadvisable because any improvement in performance typically does not keeppace with the added costs.

Not all water-soluble potassium salts can be used to obtain the resultsof the present invention. Some salts, such as those formed by reactionof a strong base (e.g. KOH) and a weak acid (e.g. H₂ CO₃), provide anundesired buffering capacity to the reaction mixture that necessitateshigher levels of caustic addition. Potassium carbonate also tends tohave an adverse affect on resole solution stability, even at lowaddition levels. Other water-soluble salts, such as potassium nitrateand potassium permanganate, are strong oxidizing agents and adverselyaffect the plywood adhesive composition.

For plywood preparation, the resin prepared in accordance with thepresent invention typically exhibits a number average molecular weightin the range of about 3,000 to 5,000 and a weight average molecularweight of about 25,000 to 50,000. The resin's polydispersity ispreferably between about 7 and 14. Preferably, the resin exhibits anumber average molecular weight in the range of about 3,700 to 4,500 andmore preferably from about 4,000 to 4,300, and exhibits a polydisperityof between about 8 to 12.

The process of making the potassium-modified resole resin of the presentinvention is directly adaptable to equipment conventionally used formaking phenol-formaldehyde resole resins. As noted above, the reactionis conducted in aqueous solution. Normally, the reaction is conducted sothat the ultimate resole resin has a non-volatile material (NVM) contentof at least about 35% by weight based on the weight of the resole resinsolution. NVM contents of up to about 55-60% are possible, although itis preferred that the NVM content not exceed about 50% in order to avoidsolutions that have such high viscosities that they present problems inmixing and pumping. Preferably, resole resin solutions useful inpreparing adhesives for making plywood have an NVM content of betweenabout 40% and 48% by weight, and more preferably between about 40% and44% by weight.

In using the resole resin of the present invention for preparing a woodcomposite such as plywood, it is common to blend the resin withadditional ingredients to prepare the actual adhesive. In addition tothe resin solution itself, which constitutes the major component of theadhesive mixture (generally from about 40 to 80% by weight of theadhesive), it is common to include various fillers, i.e. inert materialsadded to increase the weight of the adhesive mixture, adhesiveextenders, additional caustic and other known adjuvants. Generally, asuitable adhesive will contain from about 23 to 32% resin solids, fromabout 3 to 7% fillers, from about 3 to 7% extenders and from about 1 to3% additional alkaline catalysts. Suitable fillers and extenders includestarch, wood, flour, nut shell flour, bark products or agriculturalresidues, clays, and corn husks. Starch and clays generally are used asfillers, often in amounts of 1% to 10% based on the weight of the resinsolids. On a water-free basis the adhesive generally contains about 55to 75% resin solids.

In accordance with one process of the present invention, an adhesivemixture is applied to the mating surface of a plurality of wood plys.The amount of adhesive normally depends on the characteristics of theveneer to be bonded and the properties desired in the consolidatedpanel. The adhesive is applied to the plys generally in an amount ofbetween about 40 to 130 and more preferably in an amount of about 60 to120 pounds per 1000 square feet of double glue line. The applicationrates typically will differ with different wood sources. For examplesouthern pine which has a higher absorbancy capacity than westernveneers such as Douglas Fir, requires greater adhesive spreads.

The adhesive mix can be applied to the wood using conventionalequipment, including spray nozzles, atomizing wheels, roll coaters,curtain coaters, foam applicators and the like.

The various plys are assembled into a panel and generally areconsolidated at an ambient temperature, i.e., at a temperature of fromabout 15° to 30° C., and at a pressure sufficient merely to assemble theplys into a coherent article. Generally, a pressure in the range ofabout 25 to 400 pounds per square inch is suitable. The plys aresubjected to such pressure until a sufficient initial pre-pressed bondis obtained to keep the plys from separating or coming apart uponrelease of the pressure. A bond of the required strength usually isobtained with a contact time in the range of about 30 seconds to 20minutes.

After this initial consolidation, the pressure on the panels is releasedand they are stored until they are consolidated at an elevatedtemperature at which the adhesive resin cures. The use of the two steppressing procedure permits easy handling and assembly line typeoperation. For the final press, the panels are typically consolidated ata temperature within the range of about 90° to 200° C. and at pressuresof about 75 to 250 pounds per square inch. The panels are subjected tothese press conditions for a time sufficient to cure the adhesive, whichfor a normal panel construction will require anywhere from about 1 toabout 20 minutes.

A wide variety of woods can be used for making plywood in accordancewith the present invention. Suitable woods include, soft woods such asSouthern pine, Douglas Fir, Ponderosa pine, aspen and the like, as wellas hard woods such as oak, walnut and birch.

A particular advantage of the present invention is that the adhesive canbe used for gluing high average moisture content veneers with reducedblowouts and other moisture induced defects. By using an adhesiveaccording to the present invention, plywood can be prepared from aplurality of veneers having an average moisture content of greater thanabout 7% and up to about 12% and higher, with spots of moisture as highas 15-20%. Usually, veneer average moisture content is targeted forabout 5% up to about 10%.

Other advantages claimed for resins prepared by using a combination ofsodium hydroxide and potassium hydroxide are similarly realized with theresin of this invention, which has the additional advantage of lowercost.

The following examples are presented to illustrate and explain theinvention. Unless otherwise indicated, all references to parts andpercentages are based on weight and all temperatures are expressed indegrees Celsius.

EXAMPLE 1

This example describes a method of preparing a phenol-formaldehyderesole resin component of an adhesive useful in practicing the method ofthe present invention which employs potassium chloride as thewater-soluble potassium salt.

The following ingredients are added to a jacketed reaction vesselequipped with a mixer: about 24 parts phenol, about 2.3 parts potassiumchloride and about 27 parts water. During the addition of theseingredients, the contents of the reaction vessel are heated to about 60°C. About 3.2 parts of a 50% by weight sodium hydroxide solution then israpidly added to the reaction mixture, while maintaining the temperatureat no greater than about 60° C. Reflux conditions are established andabout 31 parts by weight of a 50% by weight aqueous formaldehydesolution is added into the reaction mixture over a 20 to 30 minute timeperiod. The temperature of the reaction mixture is maintained at about60° C., using cooling water if required. Once the formaldehyde has beenadded, the reaction mixture is heated rapidly to about 96° C. and heldat that temperature for about 15 minutes. Thereafter the reactionmixture is cooled to about 89° C. and about 5.4 parts of a 50% by weightaqueous sodium hydroxide solution is rapidly added. The solution ispermitted to react at this temperature until the reaction mixturereaches a Gardner-Holdt viscosity of about "G". The reaction mixture iscooled to about 80° C. and held for an additional period of time untilthe reaction mixture reaches a Gardner-Hold viscosity of about "T". Athird addition of 50% by weight aqueous sodium hydroxide solution in anamount of about 6.1 parts, then is made and the reaction mixture is heldat about 80° C. until it attains a Gardner-Holdt viscosity of about T-U.The reaction mixture then is cooled rapidly to less than about 30° C.

The resulting aqueous resin solution typically has a nonvolatilematerial content of about 43% by weight, and an alkalinity of about7.4%. Analysis of the resulting resin by gel permeation chromatographyusing a 1,000/5 weight ratio dimethyl formamide (DMF) to ammoniumformate solvent and polyethylene and polyethylene glycol standardsindicated a weight average molecular weight of about 35,000 and a numberaverage molecular weight of about 3,800, corresponding to apolydispersity of about 9. A chromatogram of this resin is illustratedin FIG. 1.

EXAMPLE 2

This example describes a method of preparing a phenol-formaldehyderesole resin component of an adhesive useful in practicing the method ofthe present invention wherein potassium sulfate is the water-solublepotassium salt.

The following ingredients are added to a jacketed reaction vesselequipped with a mixer: about 23 parts phenol, about 2.7 parts potassiumsulfate and about 28 parts water. The mixture is heated to a temperatureof about 60° C. During the heating, about 2.8 parts of a 50% by weightaqueous solution of sodium hydroxide is added rapidly to the reactionmixture. When the temperature of the reaction mixture reaches about 60°C., about 30 parts of a 50% by weight aqueous formaldehyde solution isadded to the reaction mixture over a period of about 20 to 30 minutes.Reflux conditions are established and the temperature is maintained atabout 60° C., using cooling water if required. Once the formaldehydeaddition is complete, the reaction mixture is heated rapidly to about96° C. and held at that temperature for about 15 minutes. The reactionmixture then is cooled to about 90° C. and about 5.9 parts of the 50% byweight aqueous sodium hydroxide solution is added rapidly whilecontrolling the temperature of the reaction mixture at about 90° C. Thereaction mixture is held at that temperature for an additional period oftime to allow it to reach a Gardner-Holdt viscosity of about "G". Thereaction mixture then is cooled to about 81° C. and held until itattains a Gardner-Holdt viscosity of about "T". At that time, anadditional 6.2 parts of 50% by weight aqueous sodium hydroxide solutionis added to the reaction mixture, which is allowed to increase intemperature to about 89° C. The reaction mixture is held at thattemperature until it attains a Gardner-Holdt viscosity of about "T-U"and thereafter the reaction mixture is cooled rapidly to less than about30° C.

The aqueous resole resin solution typically has a nonvolatile materialcontent of about 43% by weight and an alkalinity of about 7.4%. Analysisof the resulting resin by gel permeation chromatography using the samesolvent and standards used in the analysis of the Example 1 resole resinindicated a weight average molecular weight of about 37,000 and a numberaverage molecular weight of about 4,000, corresponding to apolydispersity of about 9. A chromatogram is illustrated in FIG. 2.

EXAMPLE 3

This example describes the use of the aqueous phenol-formaldehyde resoleresin solution of Example 1 for preparing an adhesive and using thatadhesive for making plywood.

A plywood adhesive was prepared by blending about 20 parts by weightwater with about 3.6 parts of Modal extender, about 4 parts wheat flourand about 25 parts of the resole resin solution of Example 1. Afterthrough mixing, about 2.1 parts of additional Modal extender and 1.5parts of a paper coating clay is added. After further mixing, about 2.7parts of a 50% by weight aqueous sodium hydroxide solution, 0.8 part ofsodium carbonate and a small amount of borax is added. Finally, anadditional 39.4 parts of the resole resin of Example 1 is added tocomplete the adhesive.

This adhesive was used to glue 1/8-inch thick Douglas Fir veneer havingan average moisture content of about 8 to 12%. The adhesive was appliedto the veneer by a spray line at an application level of about 62 to 72lbs. per 1,000 square feet of double glueline. Three-ply panels wereprepared. The consolidated veneer panels were pre-pressed at ambienttemperature for about 41/2 minutes at 160 psia. Thereafter, thepre-pressed panels were hot pressed at about 157° C. and 175 psia forabout one minute and then at about 157° C. and 125 psia to cure theadhesive. The consolidated boards were hot stacked for about 4-8 hoursand afterwards were subjected to vacuum-pressure testing in accordancewith the American Plywood Association (APA) procedure for measuring woodfailure. Eight randomly sampled panels were tested. The tested panelsexhibited an average wood failure of about 86%. A high wood failureindicates improved bond strength, since lower wood failures areindicative of a high incidence of glueline failure.

COMPARATIVE EXAMPLE 1

This example illustrates the preparation of an aqueous resole resinsolution by reacting phenol and formaldehyde at a mol ratio (P:F) ofabout 1:2.05 in the presence of an alkaline catalyst mixture of sodiumhydroxide and potassium hydroxide.

The following ingredients are added to a jacketed reaction vesselequipped with a mixer: about 24.8 parts of phenol and about 25 parts ofwater. The contents of the reactor are heated to about 40° C. and about6.7 parts of a 45% by weight aqueous potassium hydroxide solution isadded over a time period of about 15 minutes while the reaction mixtureis heated to about 60° C. About 32.4 parts of a 50% by weight aqueousformaldehyde solution then is added slowly into the reaction mixtureover about a 30 minute period while maintaining the temperature of thereaction mixture at about 60° C. Thereafter, the reaction mixture israpidly heated to about 96° C. and reacted for about 15 minutes. Thereaction mixture is cooled to about 80° C. over about a 10 minute timeperiod and an additional 2.6 parts of the 45% by weight aqueouspotassium hydroxide solution is added rapidly. Thereafter, about 2.9parts of a 50% by weight aqueous sodium hydroxide solution is rapidlyadded while allowing the reaction mixture to increase in temperature toabout 90° C. The reaction mixture is held at 90° C. until it attains aGardner-Holdt viscosity of about "R-S". An additional 5.1 parts of a 50%by weight aqueous sodium hydroxide solution is added to the reactionmixture while cooling it to 85° C. The reaction mixture is held at 85°C. until it attains a Gardner-Holdt viscosity of about "S". The reactionmixture then is rapidly cooled to below 40° C.

The resulting resin has a nonvolatile material content of about 43% byweight and an alkalinity of about 7.4%. Analysis of the resin by gelpermeation chromatography using the same solvent and standards used inthe analysis of the Example 1 resole resin indicated that the resin hada weight average molecular weight of about 42,000 and a number averagemolecular weight of about 4,100 corresponding to a polydispersity ofabout 10. FIG. 3 illustrates a chromatogram of this resin.

Comparing the results of Examples 1 and 2 and Comparative Example 1, itis evident that a phenol-formaldehyde resole resin having substantiallythe same molecular distribution is obtained using only about 12 mol %potassium, based on mols of phenol, when the teachings of the presentinvention are employed (i.e. when using a water-soluble potassium salt),while about 28 mol % potassium, based on mols of phenol, is requiredwhen using potassium hydroxide as the potassium source, i.e. over twiceas much potassium.

While certain specific embodiments of the invention have been describedwith particularly herein, it will be recognized that variousmodifications thereof will occur to those skilled in the art and it isto be understood that such modifications and variations are to beincluded within the preview of this application and the spirit and scopeof the appended claims.

I claim:
 1. An aqueous phenol-formaldehyde resole resin solutionprepared by reacting at least an equal molar amount of formaldehyde withphenol in the presence of (i) sufficient sodium hydroxide to provide afinal resin solution alkalinity of between about 1 to 15%, and (ii)between about 0.01 to 0.25 mol potassium per mol of phenol, wherein saidpotassium is added as a water-soluble potassium salt selected from thegroup consisting of potassium chloride, potassium sulfate and mixturesthereof.
 2. The resole resin of claim 1 wherein said phenol andformaldehyde are reacted in a molar ratio of phenol to formaldehyde inthe range of about 1:1.5 to about 1:3, said final resin alkalinity isbetween about 3 to 9% and about 0.03 to 0.2 mol potassium per mol ofphenol is present.
 3. The resole resin of claim 2 wherein said potassiumis present in an amount between about 0.05 to 0.15 mol of potassium permol of phenol.
 4. The resole resin of claim 3 wherein said final resinalkalinity is between about 4% to 8%.
 5. The resole resin of claim 4having a non-volatile material (NVM) content of between about 40 and 48%by weight.
 6. In a process for making an aqueous phenol-formaldehyderesole resin solution by reacting at least an equal molar amount offormaldehyde with phenol in the presence of sufficient sodium hydroxideto provide a final resin alkalinity of between about 1 to 15%, theimprovement which comprises conducting at least part of said reaction inthe presence of between about 0.01 to 0.25 mol potassium per mol ofphenol, wherein said potassium is added as a water-soluble potassiumsalt selected from the group consisting of potassium chloride, potassiumsulfate and mixtures thereof.
 7. The process of claim 6 wherein saidphenol and formaldehyde are reacted in a molar ratio of phenol toformaldehyde in the range of about 1:1.5 to about 1:3, said final resinalkalinity is between about 3 to 9% and about 0.03 to 0.2 mol potassiumper mol of phenol is present.
 8. The process of claim 7 wherein saidpotassium is present in an amount between about 0.05 to 0.5 mol ofpotassium per mol of phenol.
 9. The process of claim 8 wherein saidfinal resin alkalinity is between about 4% to 8%.
 10. The process ofclaim 9 wherein said aqueous resole resin solution has a non-volatilematerial content of between about 40 and 48% by weight.
 11. An adhesivecomposition suitable for making plywood comprising between about 40 to80% by weight of the aqueous resole resin of solution of claim
 5. 12.The resole resin of claim 1 having a non-volatile material (NVM) contentof between about 40 and 48% by weight.
 13. An adhesive compositionsuitable for preparing a wood composite comprising between about 40 to80% by weight of the aqueous resole resin solution of claim
 12. 14. Theresole resin of claim 2 having a non-volatile material (NVM) content ofbetween about 40 and 48% by weight.
 15. An adhesive composition suitablefor preparing a wood composite comprising between about 40 to 80% byweight of the resole resin of claim 14.